The present invention relates generally to folders of printing presses and more specifically to folders having a detection system for paper jams and a method for detecting such paper jams.
U.S. Pat. No. 4,578,052 describes a method and apparatus to determine deviations in folded sheets. The apparatus has sensors to test the folds of the folded sheet based on markings on the sheets. The apparatus however requires that the signatures be specially marked and merely tests if the folds after each folding step were properly made. The apparatus does not sense the edge of the signatures.
U.S. Pat. No. 4,573,671 describes a device for slowing down signatures before folding a signature in a chopper folder. No deviations are detected within the folder device;
Both U.S. Pat. No. 4,578,052 and 4,573,671 are hereby incorporated by reference herein.
The present invention provides a folder for processing a stream of signatures having a desired path with a path edge and each signature having a lead and trail edge. The folder comprises a plurality of sensor sets, with each sensor set determining if the lead and edge of the signature deviates from the path edge by a certain tolerance.
The present invention therefore provides for quick and easy monitoring of an entire stream of sheets or signatures in the folder. No markings on the signatures are required. An early and quick detection of possible problems in the folder is thus ensured. If press operators are forewarned of excessive signature to signature deviations, then they may correct the deviations before a jam occurs or products are wasted.
Preferably, each sensor set comprises a pair of laser emitters and a pair of diode receivers for sensing the edge of the signature.
Advantageously, when an excessive deviation is determined, the press is slowed down automatically to permit correction by the operator.
Outputs of the sensors are wired into a terminal block or box which will accept a port connector from a data acquisition card. A personal computer having a standard microprocessor and the data acquisition card with related software then can analyze the output of the sensors to identify a skew or gap variation. A monitor of a computer can provide information as to where the error in the folder has occurred. By having multiple sets of sensors in the folder, the problem area can be quickly determined by the operator.
The folder also comprises a cutting cylinder. One of the plurality of sensor sets can be located right after the cutting cylinder.
The desired path and spacing of the signatures can be predetermined by the operator, as can the amount of permissible error or deviation, i.e. the system tolerance. The desired path also could be determined based on a sampling of signatures, with the system tolerance being determined based on a standard deviation statistical analysis.
The present invention also provides a method for detecting deviations in a stream of signatures in a folder, the stream of signatures having a desired path with a path edge and each signature having a lead and trail edges the method comprising the steps of sensing the lead and/or trail edge of the signature in a plurality of locations within the folder and outputting an error message if the lead and/or trail edge of the signature deviates from the path edge by more than a tolerance.
The method further comprises the step of automatically slowing down the stream of signatures upon detection of the error message. This then prevents an excessive amount of printed signatures from being unusable and results in substantial savings in paper and other materials.
The outputted error message may identify one of the plurality of locations in which the deviation occurred.
The method further comprises The step of predetermining the tolerance,